Jason/remove bom

Browserify will remove Byte Order Marks when it bundles a package.
see https://github.com/substack/node-browserify/issues/313 for some discussion on this.

But shiming the same file preserves the BOM and moves it down from the first character in the file. 
This makes it difficult to remove with build tools.

This PR removes BOMs from packages before they are shimmed. I didn't add any configuration flag since browserify itself doesn't seem to either.